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Improve Quality Using Model Tolerances

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Introduction

This Plunger assembly design will be used to study thevalidation tools Autodesk Inventor provides. Applyingtolerances to your design within the design processgives you the ability to validate your design throughout itsdevelopment cycle, instead of waiting until 2D drawingsare produced. We will explore this technique togetherwith Inventors interference detection tools enabling youto improve the quality of your design.

There are several components internal to this PlungerAssembly that we will be looking at.

Plunger Body

Plunger

Diaphram

Parameter Tolerances

As you build up a model you have the ability to assign tolerances to each dimension/parameter that you use to describe yourpart. There are two ways in which you can apply the tolerance depending on the type of parameter generated. Each parametercan be set to the Upper, Nominal or Lower tolerance to then be used to evaluate your design.

The process to assign tolerances is described next:

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Sketch Dimensions By right mouse clicking on anysketch dimension you will have an option to selectdimension properties.

The dimension properties dialog box is shown here to theright. Within the dialog box you have the ability to apply atolerance type for this dimension.

You can drop down the list of tolerance types shown here.

Once you have applied a tolerance type you can thenassign the tolerance values.

On the top right of the dialog box you have three symbolsrepresenting the Upper, Nominal, and Lower tolerancevalues. Once you set the appropriate Evaluated size this

will change the size of the physical model to equal theUpper or Lower tolerance values specified.

Feature Dimensions The only way to add tolerances to parameters generated as a result of a feature is to go through the

Parameters dialog box. You can access this from the Panel Bar with the button. An example of a featuregenerated parameter is an Extrusion length.

In the parameter dialog box youcan right mouse click in theequation column of the desiredparameter and select theTolerance option. This willdisplay the Dimension Propertydialog box as discussed in theprevious example.

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Exercise 1: Sketch Dimension Tolerances

Open the file 1 Sketch Tolerance.ipt

Select the Revolve feature in the browser and edit thesketch.

You can then select the dimension shown in theimage and right click to select the DimensionProperties option.

In the dimension properties dialog box you can createa symmetrical tolerance of .010 and set the dimensionto the Upper tolerance then select OK.

You will then have to select the Update button

.

When you measure the surface that has beenchanged you will notice that the physical modelactually represents the Max tolerance condition asspecified (6.106 mm).

Tolerance Defaults

Just about all 2D drawings that I see have a standard toleranceblock which assigns standard tolerances to dimensions on thedrawing depending on the precision of the dimension. An exampleis illustrated to the right:

You can now take advantage of these standard tolerances withinthe modeling environment. By establishing a standard tolerancelike this within your IPT template file you can ensure that all partscreated will have these tolerances applied as dimensions andfeatures are created.

To access and specify your default tolerances open up your standard IPT template file.

Note: By opening the template file and applying your tolerances in the Default Tolerance window it will enforce these tolerancesas your parts are built in the future.

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Once your IPT template file is open go to the Tools menu >Document Settings > and select the Default Tolerance tab.

Use Standard Tolerancing Values-

Select check box to use the precision andtolerance values set on this tab whencreating dimensions.

This has to be checked in order to addtolerances.

Export Standard Tolerance Values-Select check box to export dimensions todrawings using the precision and tolerancevalues set on this tab.

If you check this, all custom tolerances will

still show in the drawing.

In the Linear/Angular area you can add tolerances basedon dimension precision, matching your current standardtolerances.

Select OK in the dialog box and save the file.

Now as you add features and sketch dimensions to a partthey will all have tolerances assigned to them.

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Applying Minimum and Maximum Tolerance Conditions

Minimum and maximum tolerance conditions can be applied to your parts at any time. In order to do this select the parameters

button in the Panel Bar.

In the Parameters dialog box there is a Tol. (Tolerance) column. By selecting the column you can select the Upper, Nominal orLower tolerance for each parameter.

On the bottom of the dialog box there is an option to Reset Tolerance. When you select one of these options it will apply to allparameters of your part. This allows you to easily turn your entire part into a Minimum/Maximum condition.

Excercise 2:

Open the file 2 Apply Tolerance.iam

This is the Plunger assembly. We will check the upper tolerance for the grey shaft thatgoes through the Plunger by utilizing the interference detection tool.

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Next go ahead and create a half section view of the assembly by using the XY plane and the assembly section tool in the Panelbar.

When your section is complete activate the grey shaft (61100500.ipt) by

double clicking on it.

Then select the parameters button in the Panel bar.

Next we will now change all of the parameters for the shaft to represent theUpper/Max tolerance value. Select the plus sign in the Reset Tolerance areaof the dialog box.

This changes all parameter to the Upper tolerance value. Close the dialog box and select the update button .This changes your model to represent the desired tolerance case.

We can now right click and select Finish Edit taking us back to the assembly.

Next go ahead and select the Analyze Interference tool , in the Tools menu.

Select the inner shaft (61100500.ipt) and the outerhousing (61411000.ipt) and then select OK.

This now shows that if the shaft was manufacturedto the maximum tolerance and the housing wasmanufactured to the nominal tolerance there wouldbe problems.

Note: When the shaft was set to the nominal

tolerance there was no interference.

In order to fix this we will have to modify and tightenthe tolerance for the shaft diameter.

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Activate the inner shaft and edit the sketch forthe feature Revolution1 in the browser.

Right click on the dimension which defines theOD of the shaft as shown in the image andselect the Dimension Properties option.

The Dimension Property dialog box allows us to overridethe Default tolerance. We can see what the currentdefault tolerance is by selecting the Document Settingstab.

The current default tolerance is .03 mm. Select theDimension settings tab so that we can now override thattolerance for this dimension.

Drop down the Tolerance Type list and select Deviation.We will now apply an upper tolerance of .00mm and alower tolerance of .03mm.

You can now close the dialog box and return to theassembly to re-run the Interference detection.

Try applying tolerances to the housing and checking theworst case tolerance settings on the housing and theshaft.

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Retrieving Dimensions in the Drawing

All dimensions with or without tolerances that were created in the model can be re-used in the drawing (IDW) by utilizing theRetrieve dimension tool.

Exercise 3

Open the file 61100500.idw .

Some standard views of the shaft have already been created. Select the front view of the shaft and right click. In the right clickmenu select the Retrieve Dimensions option.

In the retrieve dimension dialog box under Select Source you can choose whether you want to retrieve dimensions for the entirepart or individual features of the part. By default it is on Select Features so select the Revolve feature in the front view (an objectline).

All of the dimensions for the Revolve feature will then show up in the view.

Next by selecting the Select Dimensions button in the dialog box you can choose which dimensions you want to keep on thedrawing.

Select the dimensions with tolerances and then OK. By reusing the dimensions with tolerances from the model you have savedtime and know that the tolerance values have already been validated with mating components.

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Take advantage of the ability to capture tolerances in the design process then use them while validating yourassemblies. This will hopefully improve the quality of your product as well as save you time and increasedconfidence when creating your drawings.

Thank you for attending this class. Feel free to contact me with questions - [email protected]

For Tips and Tricks visit: www.ketivtech.com

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